Small capacity tubular adjustable condenser



May 22, 1956 c. L. SHULL 2,747,147

SMALL CAPACITY TUBULAR ADJUSTABLE CONDENSER Filed Jan* 4, 1954 JNVENTOR.4a/Zw OC. ifi/@4L AT RNEY `VIIIIA WI TNESS l United States `Patent OSMALL CAPACITY TUBULAR ADJUSTABLE CONDENSER Charles L. Shull,Horseheads, N. Y.

Application January 4, 1954, Serial No. 401,809

Claims. (Cl. 317-249) The present invention relates to a small capacitytubular adjustable condenser, and more particularly to a trimmercondenser for high frequency oscillating electronic circuits.

In order to secure accurate and stable adjustment and quiet operation ofelectronic devices incorporatingA oscillating circuits, it is necessarythat the adjusting condensers operate smoothly, without either loosenessor jamming; that lost motion or'backlash be prevented, and thatcontinuous firm electrical connections be maintained at all times.Considerable difiiculty has heretofore been encountered in providing aneconomical form of trimmer condenser which meets these requirements.

It is an object of the present invention to provide a novel trimmercondenser which is adapted for accurate and stable adjustment, whilebeing simple in structure and economical to manufacture.

It is another object to provide such a device which is free from lostmotion during reversal of direction of adjustment. i

It is another object to provide such a device in which adjustment of thecondenser is accomplished without breaking or disturbing the electricalconnections of the movable element, firm electrical contact beingmaintained at all times.

Further objects and advantages will be apparent from the followingdescription taken in connection with the accompanying drawing, in which:

Fig. 1 is a vertical substantially mid-sectional view of a preferredembodiment of the invention;

Fig. 2 is a detail in elevation of the inner electrode; and

Fig. 3 is a view similar to Fig. 1 of a modified form of the invention.

In Fig. 1 of the drawing there is illustrated a hollow cylinder 1 ofsuitable dielectric material such as glass or other ceramic materialhaving an exterior metallic sheath 2 extending from one end of thecylinder for a distance somewhat less than half its length. The sheath 2constitutes the outer electrode of the condenser and is formed with acap 3 having an arm 4 for making electrical connection.

A hollow metallic mounting bushing 5 is rigidly connected in anysuitable manner as indicated at 6 to the other end of the dielectrictube 1, said bushing being exteriorly threaded for the reception of anut 7 by which the bushing may be rigidly mounted in a panel 8 or thelike.

The bushing 5 is provided with an interior annular shoulder 9 having anoutwardly facing concave spherical bearing surface 11. A screw shaft 12is loosely mounted at one end in the bushing 5 and is provided with ahead 13 rigidly mounted thereon as by means of a press-fit, and providedwith a convex spherical surface 14 mating with the surface 11 of thebushing. The bushing is preferably provided with an annular ange 15which is loosely constricted around a shoulder 16 on the head 13 to forma swivel connection for the shaft 12 in the bushing. The screw shaft 12extends into the dielectric tube 1, and an inner electrode 17 having asliding fit within the dielectric tube 1 is threaded on the shaft 12 forlongi* tudinal adjustment by rotation of the shaft, as by means of ascrew driver slot 18 formed in the head 13.

The inner electrode 17 is counterbored for a major portion of its lengthas indicated at 19, and the bushing S is provided with a similarcounterbore 20. A compression spring 21 of electrically conductivematerial such as Phosphor bronze is received at its ends in thecounterbores of the inner electrode and bushing and is assembled underpressure whereby it serves to hold the spherical surfaces 11, 14 of thebushing 5 and head 13 firmly in contact at all times.

The inner electrode 17 is provided with an axially extending socket 22,and the shoulder 9 of bushing 5 is provided with a similar socket 23.The spring 21 has its terminal portions bent axially and seated in saidsockets 22, 23 whereby the spring resists rotation of the innerelectrode and at the same time makes a rm continuous electricalconnection to the bushing 5.

In order to stabilize the inner electrode in the dielectric tube andprevent loss of adjustment by reason of vibration or shock, it isprovided with a chordal slot 24 which extends from its open end as bestshown in Fig. 2, thus forming an arm 25 separated from the body of theelectrode except at its lower end. The arm 25 is sprung outwardly asshown in dotted lines in Fig. 2 whereby, when the electrode is insertedin the tube 1, the arm bears frictionally in the tube and preventslateral movement or vibration of the electrode and also resists itsrotation in the tube.

In operation, when the condenser is incorporated in an electricalcircuit, one connection is made by means of the connector arm 4, and theother connection by grounding the bushing 5 or in any other suitablemanner. Rotation of the head 13 and screw shaft 12 causes longitudinalmovement of the inner electrode 17 to bring it more or less intoregistry with the outer electrode 2 whereby the capacity of thecondenser is varied as desired. During this adjustment, and at all othertimes, the spring 21 performs the three functions of holding the thrustbearing surfaces 11, 14 in firm contact, preventing lost motion betweenthe threads of the screw shaft 12 and inner electrode 17, and resistingrotation of the inner electrode so as to insure its traversal when thescrew shaft is rotated. At the same time, the pressure of the spring arm25 against the interior of the dielectric tube 1 insures a firm slidingfit of the electrode in the tube and further assists in preventingrotation of the inner electrode. The spherical shape of the thrustbearing surfaces 11, 14 permits the screw shaft to adjust itselfangularly in the bushing 5 to compensate for any slight misalignment ofthe dielectric tube 1.

Fig. 3 of the drawing shows an embodiment of the invention in whichstabilization of the inner electrode is accomplished by means of thestabilizing spring disclosed in applicants prior application Serial No.263,540, filed December 27, 1951. As there shown an elastic spidermember 26 is rigidly mounted on a reduced terminal portion 27 of saidelectrode as by means of a spinning operation as indicated at 28. Theelectrode has a tapered section 29 adjacent the reduced portion 27, andthe spider 26 is formed with a plurality of divergent spring arms 30which embrace said tapered section when compressed by introduction ofthe electrode into the dielectric tube 1.

The pressure of the arms 30 against the interior of the dielectric tubehas been found in practice to stabilize the electrode against all butdestructive shocks.

Although structure has been shown and described in detail, it will beunderstood that changes may be made afnam? in the precise form andarrangement of the parts without departing from the spirit of theinvention.

I claim:

1. In a tubular trimmer condenser a dielectric tube having an 'exteriormetallic sheath for a portion ofits length forming the outer electrode,a hollow metallic mounting bushing -iXedly attached to one end of thetube, a screw shaft swivelled in the bushing with freedom for limiteduniversal movement, an inner velectrode threaded on the screw shaft andslidable in the tube into and out of registry with the outer electrode,said bushing and inner electrode having coaxial facing coonterbores, andmeans including a'm'etallic compression spring loosely surrounding thescrew shaft seated in said counterbores and nonrotatably anchored at itsends to the bushing and inner electrode respectively, for exerting axialpressure thereon to compress the universal connection, to resistrotation of the inner electrode, and to form a rm stationary continuouselectrical connection between the bushing and inner electrode.

2. A trimmer condenser as set forth in claim l in which the swivelconnection between the bushing and screw shaft comprises a head on thescrew shaft having a convex thrust surface, said bushing having a matingconcave thrust surface, the pressure of said spring Servf ing to holdsaid thrust surfaces in contact.

3. A tubular condenser as set forth in claim l in which said bushing andinner electrode are provided with axially extending recesses, `and saidspring is provided with outturned ends seating in the recesses andresisting rotary movement of the inner electrode in the dielectric tube.

4. A tubular condenser as set forth in claim 1 including furtherexpansive spring means on said inner electrode bearing frictionallyagainst the inner surface of the dielectric tube to stabilize said'electrode against vibration.

5. A tubular condenser as set forth in claim l in which the innerelectrode is in the form of a hollow cylinder having a chordal slotforming an elastic arm which is sprung out to press against the interiorof the dielectric tube to resist lateral movement and rotation of theinner electrode in the tube.

References Cited in the file of this patent UNITED STATES PATENTS2,411,810 Sander Nov. 26, 1946 2,607,826 Barnes Aug. 19, -1952 FOREIGNPATENTS 263,948 Great Britain 1an. 10, 1927 496,315 Great Britain e Nov.l29, 19.38 628,499 Germany Apr. 6, 1936

